Two-beam Interferometry Research Articles

Quasi-object-adapted variable-wavelength double-refracting microscope interferometry

A specific interterometric method has been developed. The method uses monochromatic light of continuously variable wavelength through the visible spectrum, and thus is referred to as variable-wavelength interferometry (VAWl). In some special circumstances, the VAWI method takes a specific form, referred to as object-adapted (or adaptive) variable-wavelength interferometry (AVAWI), which enables the optical path difference or phase retardation and derived quantities to be measured very precisely by relatively simple means. In practice, however, the most frequent interlerometric situations at the microscopic level can be qualified as the quasi-object-adapted ones. Therefore, a modified approach to quasi-object-adapted variable-wavelength interferometry (QAVAWI), its features, and performance is presented. In general, the VAWI method is much more accurate than conventional visual two-beam interferometry techniques. In particular, the AVAWI version enables the measuring accuracy of the optical path difference to be improved by two orders of magnitude, while the QAVAWI procedure offers better accuracy by at least one order of magnitude.

銅単結晶(111)面の溶解に及ぼすヤング腐食液中の過硫酸アンモンおよびアンモニア水濃度の影響

The effect of the concentration of (NH4)2S2O8 and NH4OH on dissolution of the copper (111) surface in Young’s etchant ((NH4)2S2O8-NH4OH-NH4Br) was studied by utilizing the etch-pits of edge dislocations. The dissolved thickness S of the matrix surface was first measured by two-beam interferometry. The two quantities H and D correlating with the dissolution of the copper (111) surface in lateral and normal directions at the dislocation sites were determined from S and the width h and depth d of the edge dislocation etch pit which were measured by replica electron microscopy.As the concentration of (NH4)2S2O8 and NH4OH in the etchants was increased, the following features were confirmed: (a) the lateral dissolution at the edge dislocation sites, H, increased gradually, (b) the normal dissolution at the edge dislocation site, D, showed a maximum at a certain concentration and (c) the matrix dissolution, S, increased slightly.These results were discussed on the basis of the two-dimensional nucleation theory of crystal dissolution.

Noncontacting detection in ultrasonic nondestructive evaluation of materials: Simple optical sensor and fiber-optic interferometric application

An optical displacement sensor based on the two-beam interferometry of coherent light using two principal diffracted orders of a fine reflection blazed grating is constructed. The inherent capability of the interferometer for absolute calibration, its maximum sensitivity adjustment, and the simplicity of the configuration of its components are explained. Utilization of a single-mode optical fiber in the test arm of the interferometer to enhance the geometric flexibility of the optical system is demonstrated. The sensor’s application in the noncontacting detection of stimulated ultrasonic stress waves for nondestructive evaluation of advanced composite materials is emphasized. The detected signal is digitized and recorded using an IBM PC with a plug-in data-acquisition board. The combination of high sampling rate capability of the device and optical detection has facilitated the signal processing of ultrasonic waves in order to achieve interpretation and quantification of the physical parameter of interest (i.e., displacement).

“Billet and Meslin bi-lenses” in two-beam X-ray interferometry

The problem of the interference patterns of X-ray interferometers, when the primary beam is a monochromatic X-ray radiation from pointsources is discussed. In this case the diffraction of the beam for vacuum propagation is discussed. X-ray two-beam interferometer with narrow interplane thicknesses, three-block defocused and three-block different thickness systems are used. The analogue is shown of the first two interferometers with the known “Billet bi-lens” system and of the third one with the “Meslin bi-lens” system. [Russian Text Ignored].

Visualization of antiferromagnetic domain structures on as-grown NiO crystals by optical methods

The antiferromagnetic T-domain structures on a bulk NiO crystal surface could be visualized by means of incident-light types of microscope such as a differential interference microscope, a phase-contrast microscope and a high-dispersion interference contrast method. The visualization of the antiferromagnetic domain is possible due to the facial tilt which was induced in the NiO crystal due to the antiferromagnetic ordering below the Neel temperature. The lateral resolution of the present methods in visualization of the domain structure is about 1μm, which is better than that of X-ray or neutron topography. The tilt angle between each domain was measured by two-beam interferometry; the average experimental value (9′23″) agrees fairly well with the calculated value (8′24″). Direct observation of the movement and disappearance of the domain boundaries upon heating could also be carried out under the phase-contrast microscope.

The Refractive Index and the Exciton Transition Oscillator Strength of CdSe Single Crystals

AbstractThe dependences of the refractive index and the group velocity of light on the photon energy are obtained near the exciton transitions of CdSe single crystals at 5 K by the method of twobeam interferometry. The independence of the oscillator strength on the sample thickness is determined for the exciton transitions in CdSe. The results are compared with the data obtained by other's methods in recent papers.

White Light Fringes and Dispersion in Two-beam Interferometry

In two-beam interferometry, if the difference in optical paths is a linear function of wavelength, then spurious white light fringes of high order are formed.

Measurement of surface topography of magnetic tapes by Mirau interferometry

Stylus-profiling techniques cannot be used for surface characterization of polymeric surfaces, such as magnetic tapes, because of their relatively low hardness. An interferometric-optical-profiling microscope system was used to obtain high-accuracy surface profiles of magnetic media, rapidly and without physical contact with the sample. The profilometer consists of a conventional, reflection-type optical microscope with a Mirau two-beam interferometer attachment. The interference patterns of the surface can be observed through the eyepieces and can be detected with a solid-state linear array of 1024 detector elements. By translating the reference surface of the interferometer with a piezoelectric transducer while taking consecutive measurements, accurate surface-height measurements can be obtained from each detector element. The microscope system is controlled by a microcomputer, which communicates with a desk-top computer for further analysis of the surface-profile data. A computer-controlled specimen stage is added to increase the sample size. The reasons for selecting the Mirau two-beam interferometry are also discussed. Sample data of magnetic tapes are presented. Experimental data presented in the paper show that optimization of surface roughness is necessary to obtain optimum magnetic amplitude, friction, and wear properties.

Analysis of two-beam interferometry for bulk wave measurements

The application of differential interferometry to bulk wave measurements can be analyzed using the kinematic formulation of the photoelastic effect. For isotropic linearly elastic materials, a standing longitudinal wave changes the indicatrix from a sphere to an ellipsoid of revolution with axes parallel and perpendicular to the direction of propagation of the acoustic wave. If the probing light is linearly polarized, differential interferometry produces a maximum signal when the polarization of the light is perpendicular to the direction of propagation. This prediction is confirmed by experiment. The case of standing transverse waves can be analyzed in a similar manner.

Crack nucleation and stage I propagation in high strain fatigue—I. Microscopic and interferometric observations

The details of crack nucleation phenomena in the high strain fatigue of OFHC copper have been studied by optical microscopy and two-beam interferometry. By observation of artificially rumpled specimen surfaces, the plastic instability mechanism of crack nucleation has been ruled out in polycrystalline metals in favor of one which takes into account the detailed crystallographic aspects of slip in adjoining grains. As a result of this cyclic slip, a step is gradually built up at a sensitive grain boundary until it is approximately 1.5 μm high, at which point the stress concentration of the step is sufficient to propagate a crack both along the boundary at the surface and into the bulk of the specimen.

Coherent Raman gain spectroscopy using CW laser sources

The recent demonstration of stimulated Raman gain (loss) spectroscopy (SRS) using CW laser sources introduces a powerful tool to coherent Raman spectroscopy. In this paper we undertake an experimental and analytical evaluation of several variations of SRS using CW laser sources including (1) direct stimulated Raman gain (loss) measurements, (2) optically heterodyned polarization interferometry, and (3) two-beam nonlinear interferometry. The results show CW SRS to be a convenient and effective means of obtaining direct Raman spectra in applications where background fluorescence precludes the use of conventional Raman techniques. Sensitivities comparable to or exceeding those obtained by coherent anti-Stokes Raman spectroscopy (CARS) are demonstrated. Ultimate sensitivities exceeding those achieved by spontaneous Raman spectroscopy are expected for high-resolution applications in gaseous media.

Polarizing effect of beam-splitter in two-beam interferometry

Reflection and transmission at and through a metallic film change the polarization parameters of a beam of light. This implies that the two interfering beams of two-beam interferometers using such film as beam-splitter are different so far as the state of polarization is concerned. It is shown that in the resultant interference pattern there is a periodic variation of the state of polarization along with the periodic variation of intensity. Actual numerical calculations have been made to study the nature and extent of variation of polarization parameters due to the polarizing effect of an aluminium film coated on a glass-plate.

All-Reflection Interferometer for Use as a Fourier-Transform Spectrometer*

This paper describes the design and tests of an all-reflection two-beam interferometer. The unique feature of this interferometer is the use of a combination of three diffraction gratings as a beam splitter. The use of reflection-type diffraction gratings as a beam splitter eliminates the need for transmission elements and thereby extends the applicability of two-beam interferometry to regions of the electromagnetic spectrum such as the vacuum ultraviolet where transmitting beam splitters are not available. A preliminary type of grating beam splitter using a single grating is discussed, and its disadvantages are described. Finally, an interferometer that uses three gratings as a beam splitter and which can function as an all-reflection Fourier-transform spectrometer is described. Interferograms of simple spectra taken with this instrument are presented.

Lunar Glass: Interferometric Evidence for Low-Temperature Shock

Glass objects in the fines from the Apollo 11 and Apollo 12 missions are shown, by two-beam reflection interferometry, to have been subject to shock at temperatures below the melting or softening point of the glass. Possible causes for the glass fragmentation are discussed.

On the identification of the polar surfaces of SiC crystals

The identification of the polar surfaces of silicon carbide with an alkaline solution was investigated by phase-contrast microscopy and two-beam interferometry. It is found that the alkaline solution produces growth patterns on the (0001) carbon surface, while the opposite (0001) silicon surface remains essentially unaffected. The merit of polarity determination by a growth method combined with phase-microscopy was proposed.

Activation energy of dissolution at emergent dislocations

Rates of deepening of dislocation-etch-pits at the (001) cleavage faces of single crystals of NiSO4,6H2O were measured by two-beam interferometry. By comparison with the rate of general dissolution of the surface in ethanol, it is shown that a significant decrease in activation energy (95 in 211 kJ mol–1) is associated with preferential dissolution at an emergent dislocation. It is probable that the core energy, rather than the elastic strain energy of the dislocation, is the principal cause of the decrease.

Geometrical optics treatment of fringe localization in two-beam hologram interferometry

Geometrical optics treatment of fringe localization in two-beam hologram interferometry

Holographic Interferometer for Isopachic Stress Analysis

Application of holography to photoelasticity is briefly discussed, with emphasis on its potential in isopachic stress analysis. A complete holographic interferometer is described. The method of wavefront reconstruction simplifies the optical requirements in conventional two-beam interferometry. By employing a photochromic recording medium, the technique of real-time interference becomes a practical and convenient process. Examples of isopachic fringe patterns obtained by this interferometer are shown.

3.5 - Precise interferometry of glass plates

A method employing both multiple-beam and two-beam interferometry for the measurement of extremely small changes in thickness and refractive index of glass plates is described. The glass plate which is to be measured is scanned through a narrow laser beam in one arm of a Twyman-Green interferometer, the output of which constitutes one arm of a two-beam optical measuring set. By measuring the changes in intensity of the light emerging from the interferometer (once with the interferometer mirrors in use and once with the mirrors blocked), two sets of data are obtained which permit the separate determination of the variations of thickness and refractive index. Since the optical measuring set can easily detect changes in light intensity of one part in 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> , changes in thickness of the order of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\lambda/1000</tex> and changes in refractive index of the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> can be measured. By scanning over the area of the sample, a contour diagram depicting both thickness variations and refractive index variations can be constructed.

Effects of Film Nonlinearities in Holography

A study of the effects of photographic nonlinearities in recording coherent wavefronts is reported. Particular emphasis is placed on holography using the two-beam interferometry technique. A phenomenological model which provides the mathematical formulation for describing the effects of nonlinearities is described. The model includes a zero-memory nonlinearity which represents experimentally derived transmittance-exposure curves for various photographic emulsions. An analysis of this model reveals many interesting phenomena which are supported experimentally. In particular, the nonlinearity of the film generates false targets, causes weak signal suppression, and can introduce additional noise as a result of spectral folding. Experimental results, verifying the analysis, are presented.